<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <h4>b.html</h4>

    <script>
        window.addEventListener('message',function(e){
            console.log(JSON.parse(e.data));

            if (e.data) {
                setTimeout(function() {
                    window.parent.postMessage('我接收到了','http://127.0.0.1:5500')
                }, 2000);
            }
        })
    </script>
</body>
</html>